Sorry, have no answer, I don't know anything abt this. I've been here since the beginning of this Forum & don't recall any discussion of this at all. But also, in my 10+ yrs. now of growing Hoyas I don't think I ever thought or even wondered abt this. Hummm.....

I think that hoyas vary in their required/preferred pH level. I don't think there is just one pH level for all hoyas, but I could be wrong. On Dave's Garden, in the Plant Files section, it seems that they have most hoyas having the same soil pH requirements, ranging between 6.1-6.5 (mildly acidic) to 6.6-7.5 (neutral).

If I recall correctly, H. calycina is one that sticks out in my mind as wanting more acidity. Can't remember the others, but there definitely are acid loving hoyas. Truth is, I never do anything different with the more acid loving hoyas, and they seem to do just fine. But maybe they'd do even better if I adjusted the pH levels on these certain hoyas!!

I'm attaching a link on the bottom that gives an example of pH levels for hoyas. This is for H. calycina (go to the "biology" section for pH info), but it has about 100 hoya species and info on them, including pH info. This may be helpful if you know what to do with that information!

Hi,
Gabi..Thankyou so much you have been a great help I will have quite a bit to read,it seems it does not do them any harm to just leave the soil as is but it will still be interesting to learn so thanks again for your trouble Karen...

Pirategirl...Thanks anyway just for replying I do appreciate it. Karen...

I was wondering about this recently too.
Adding lime would actually make the soil more alkaline, not acidic so I don't think it would be great for most hoyas.
That is a great link! I was frusterated because Dave's garden gave the same pH requirements for all of the hoya species and I've heard that eriostemma like it more basic.

Oh, I guess I thought lime made the soil more acidic. Either way, I remember reading that some hoyas like lime, so I guess it meant that the soil should be more alkaline. Interesting. I'm so curious to know if paying attention to pH requirements really makes a difference.

I once asked a well know hoya expert their opinion on lime for hoyas, and they said that it wasn't necessary, that all hoyas do best in a "slightly acid mix" and that if they do need a lower PH than that, they most likely get it from the purified tap water that most of us can get right from our kitchen sinks.

The standard potting mix we use for Hoyas is naturally acidic because of the addition of bark or other organic matter that will slowly break down. I believe that the only instance where you would need to adjust the pH is if you are using a completely inorganic mix like Leca or Hydrotron or if you have a plant that is normally found growing terrestrially or lithophytically in areas where limestone is the predominant type of rock.

Growing in an inert media like expanded clay means that there is no organic buffering agent available to keep the pH within an acceptable range. depending on your tap water and the type of fertilizer you use you can run into problems with pH which means that some nutrients will precipitate out of solution and be unavailable to the plants. If your plants seem to be growing fine don't worry about pH. Too much tinkering with potting mixes and things can turn into a disaster. From someone who learned the hard way what happens when you try new things with otherwise healthy plants, "If it isn't broke don't fix it".